A microporous membrane has numerous microscopic pores. These microscopic pores are connected to one another such that the back and front of the microporous membrane are connected to provide permeability. Due to this, the microporous membrane has good permeability, and thus has been used in various applications such as various separators in batteries, electrolytic capacitors, and the like, various separation membranes (filters), absorbent articles represented by diapers and sanitary goods, moisture-permeable waterproof materials for garments and medical use, materials for heat-sensitive receiving papers, and materials for ink receptors. The microporous membrane, particularly, a polyolefin microporous membrane including polyethylene or polypropylene is excellent in permeability and strength, and thus has been used as a battery separator for separating a positive electrode from a negative electrode.